A = area of ashpit opening in square feet.
V = velocity of air through ashpit in feet per min.
tz = temperature of flue gases, found by pyrometer.
/! = temperature of stokehole.
rj = absolute temp, of do.
P = pressure of atmosphere in Ibs. per sq. ft.
w = weight of i cub. ft. of air at P in Ib. units.
k = coal used per m. in Ibs.
Then, AV cub. ft. of air per m. are used, whose weight per
cub, ft. (see p. 590)
Pxi 147x144 39-4
But —T— = weight of air per Ib. of coal.
And, as Total wt. x sp. ht. x temp, rise = total heat
Heat units \ _ / AW# \ p , _
' ' wasted per Ib. of coal / ~ \ ^ / P^S~ i)
Note that Cp = specific heat of the flue gases at constant
pressure and is almost always exactly '25.
The second method may be briefly stated as follows:—
(a) Find % volumetric composition of flue gases, and con-
vert at once into % weight composition,
(i cub. ft. CO2 at 32° weighs '122 Ib
i cub. ft. N at 32° weighs '078 Ib.
i cub. ft O at 32° weighs '089 Ib.)
(b) Find weight of CO2 per Ib. of coal, thus :
. °/°^, (i Ib. C + 2-66 Ib. 0) = • °'° Ct (3:66 Ib, CO2)
(c) Hence find by proportion the total weight of each flue
gas separately, per Ib. of coal.
Cp x wt. of each gas per Ib coal x rise of temp.
the heat given to each gas may be found, and thus the
total heat given to the mixture can be deduced per Ib.
of fuel, by addition.
(Cp = -216 for C02, -238 for air, -244 for N, *2xS'fot O.)